Rhipicephalus appendiculatus: larval feeding sites in guinea pigs actively sensitized and receiving immune serum.

Histological analyses of larval Rhipicephalus appendiculatus feeding sites in naive and actively sensitized guinea pigs were made at 6, 24, 48, 72, 96 hr post-tick attachment. As primary feedings progressed the cavity at the entrance of the ticks mouthparts into the uppermost dermis, and the surrounding cellular infiltrate (lesion) both increased. Early (6 hr) lesions were dominated by eosinophils again predominated at 72 hr (44%), and finally basophils were dominant at 96 hr increased as tick feeding progressed and at each observation time was at least twice that observed in primary feedings. Dermal cavities at the site of entrance of the ticks mouthparts were occasional in occurrence and were reduced in size indicating altered tick feeding. Basophils were dominant at all observation times ranging from 61 to 91% of the infiltrate. The second cell type of significance was the eosinophil, ranging in abundance from 7 to 21%. Recipients of immune serum had a smaller cellular filtrate around feeding ticks, but basophils were also dominant. Basophils appear to be the principal host cell involved in acquired resistance to tick feeding as indicated by the profound cutaneous basophil reaction that characterized the immune response to larval ticks both in actively and passively sensitized hosts. The finding of significant eosinophil accumulations at tick feeding sites of both hosts indicates that these cells may also contribute to acquired resistance.